The interdiction of illicit drugs, explosives, and other contraband is an important goal of law enforcement. To that end, a variety of technologies have been developed and deployed for the non-intrusive inspection of objects, such as vehicles or containers, that are not readily susceptible to visual scrutiny from the outside. The non-intrusive aspect of these inspection techniques is important; the great majority of containers do not carry contraband, and the public would not long tolerate the delays, disruption (and in some cases damage) of property, and invasions of privacy that would occur if invasive inspection means were commonly used. Non-intrusive inspection is typically non-destructive and can usually be accomplished faster than intrusive inspection, thereby increasing productivity of inspectors. Increased productivity means more containers inspected and more contraband interdicted.
Among non-intrusive inspection methods, x-ray imaging in its many forms is a proven technology capable of detecting a variety of contraband. X-ray systems have been based on transmission imaging in any of a variety of implementations: cone-beam, fanbeam, flying-spot, multi-projection configurations; dual-energy imaging; computed tomography; as well as on imaging incorporating the detection of x-ray radiation scattered in various directions. Imaging using scattered x-rays detected from a mobile platform is the subject, for example, of U.S. Pat. No. 5,764,683, issued Jun. 9, 1998, which is incorporated herein by reference. Imaging using scattered x-rays detected from within a concealing enclosure is the subject, for example, of U.S. Pat. No. 7,099,434, issued Aug. 29, 2006, and U.S. Pat. No. 7,505,556, issued Mar. 17, 2009, both of which patents are incorporated herein by reference.
A weakness of inspection systems based on sideways-directed x-ray beams is that threatening materials located on the floor, in the back seat, or in the trunk of an inspected vehicle may be missed because of the side-shooting geometry and because of the amount of material (and clutter) in the beam path.
It is desirable to determine the presence of objects, such as contraband, weapons, or explosives, that have been concealed, for example, in a moving vehicle, or on a person, or in any inspected object, while the inspected object is moved past one or more systems that image the contents of the object using penetrating radiation. The determination should be capable of being made while the inspected object is in motion, or, alternatively, while the inspection system is in motion with respect to the inspected person or object. Indeed, since inspection rate, and thus hourly throughput, is at a premium, it is desirable that the vehicle, for example, be driven without requiring the driver or passengers to alight. In cases where a detection is made, a visual image should be available for verification.
Various inspection systems that have been deployed employ radiation that is incident on the inspected object and then scattered by the object and its contents in various directions. The use of images produced by detection and analysis of penetrating radiation scattered from an irradiated object, container, or vehicle is the subject, for example, of U.S. Pat. No. 6,459,764, to Chalmers et al. (the “Chalmers Patent”), issued Oct. 1, 2002, and incorporated herein by reference. The Chalmers Patent teaches backscatter inspection of a moving vehicle by illuminating the vehicle with x-rays from above or beneath the moving vehicle, as well as from the side, however, each of the backscatter systems taught therein require ponderous fixed-site installations.
The use of an x-ray source and an x-ray detector, both located in a portal, for purposes of screening personnel, is the subject, for example, of U.S. Pat. No. 6,094,072, to Smith, issued Jul. 25, 2000, and incorporated herein by reference. A portal, however, is not typically amenable to rapid and flexible deployment, but, rather, requires a dedicated installation. An inspection system providing these features is desirable.